1. Field
Aspects of the invention relate to a directional gamma radiation detector system for determining the angle under which the measured gamma radiation did hit the directional gamma radiation detector system for homeland security applications.
2. Description of the Related Art
Compact instruments providing gamma spectroscopy and radionuclide identification are known in the art. Nevertheless, those compact instruments are insensitive to the angle where the radiation is coming from. Directionality can be obtained with multi-detector arrangements or position sensitive detectors, for example with so called Compton cameras. Those are complex systems, which require complex algorithms, i.e. recursive reconstruction algorithms, and considerable computing power. Apart from the fact, that those detector systems are complex and large, the needed computer power bars those systems from any real-time applications. Instead, it is necessary to evaluate the data offline (that is, once the measurement has been completed).
Especially in homeland security applications, there is a strong need for a compact detector system, being able to provide any directional information. In contrast to imaging, as known from medical applications, directionality means not mapping of an activity distribution (as required in medical applications) but supporting the search for hidden sources by indicating the direction to the source. The minimum is a “left/right” and/or “up/down” indication, but limited angular resolution would be even better. The latter would allow displaying a pointer which points to the source and thus guides the operator to the source.
Such a directional gamma-ray radiation detector is known from US2009/0309032A1 (Ramsden). This detector system is using a multitude of, preferably four, scintillation detectors, mounted around a pointing axis, evaluating the count rates in each of the scintillators. When the gamma radiation hits the detector system under an angle, those scintillators being closer to the radiation source do shield the other scintillators at least in part, leading to a higher count rate in those scintillators.
Such a system has some severe disadvantages. First, it is necessary to use large and highly efficient scintillator materials when high energy gamma sources are to be detected, as the necessary shielding effect is decreasing with increasing energy. This makes the system large and heavy, which is a specific disadvantage when talking about portable—handheld—devices. Second, the angular resolution is very poor when the angle, under which the gamma radiation hits the detector system, is small with respect to the pointing axis.